177857809

This number is a prime.

Start at 177857809. Double and either add or subtract d = 308843535. Repeat. This can produce a sequence with a record length of 26 distinct primes.

Start number:    177857809
* 2 - d =         46872083
* 2 + d =        402587701
* 2 + d =       1114018937
* 2 + d =       2536881409
* 2 - d =       4764919283
* 2 - d =       9220995031
* 2 + d =      18750833597
* 2 - d =      37192823659
* 2 - d =      74076803783
* 2 - d =     147844764031
* 2 - d =     295380684527
* 2 + d =     591070212589
* 2 - d =    1181831581643
* 2 + d =    2363972006821
* 2 + d =    4728252857177
* 2 - d =    9456196870819
* 2 + d =   18912702585173
* 2 + d =   37825714013881
* 2 + d =   75651736871297
* 2 + d =  151303782586129
* 2 + d =  302607874015793
* 2 - d =  605215439188051
* 2 - d = 1210430569532567
* 2 - d = 2420860830221599
* 2 + d = 4841721969286733

[Seggelin and Andersen]